(function (doc, win) {
    // 以苹果6 375px为标准  1rem为10px
   var docEl = doc.documentElement
   var resizeEvt = 'orientationchange' in window ? 'orientationchange' : 'resize'
   var recalc = function () {
     var clientWidth = docEl.clientWidth
     if (!clientWidth) return
     docEl.style.fontSize = 2 * (clientWidth / 75) + 'px'
   }
   if (!doc.addEventListener) return
   win.addEventListener(resizeEvt, recalc, false)
   doc.addEventListener('DOMContentLoaded', recalc, false)
 })(document, window)